Inversion of Rayleigh wave phase and group velocities by simulated annealing

Abstract

A joint inversion of regionalized phase and group velocities of fundamental mode Rayleigh waves is performed by means of a simulated annealing scheme which makes use of some thermodynamic analogies based on the Gibbs’ distribution. The correlations and the uncertainties on shear-wave velocities defining the elastic model are estimated by using a procedure based on the same thermodynamic analogies. As a relevant feature, the simulated annealing algorithm permits reducing the usual dependence of the solution on the sometimes arbitrary starting model. A shortcoming linked to the use of this procedure for solving an inversion problem is the necessity of a previous empirical determination of some parameters controlling the annealing process. With this aim, a simulation of a joint inversion of synthetic surface wave dispersion data has been performed. After that, path-averaged velocity dispersion curves corresponding to a Hercynian area of the Iberian Peninsula have been inverted to derive two possible crust and upper mantle elastic structures. Whereas, the first structure has been deduced by considering as unknown variables the shear velocities of the stratified Earth model, the second has been obtained also including the respective layer thicknesses. Both structures are compared with shear velocity and Q β models derived by the stochastic inversion procedure in previous studies and from the same Rayleigh waves dataset. Finally, advantages and shortcomings of the inversion of phase and group velocity data by means of simulated annealing are discussed.